U.S. patent number 6,352,018 [Application Number 09/553,384] was granted by the patent office on 2002-03-05 for hydraulic actuator assembly with integral damper/accumulator.
This patent grant is currently assigned to Spicer Technology, Inc.. Invention is credited to James A. Krisher.
United States Patent |
6,352,018 |
Krisher |
March 5, 2002 |
Hydraulic actuator assembly with integral damper/accumulator
Abstract
A novel arrangement of a hydraulic actuator assembly is
disclosed. The hydraulic actuator assembly comprises a
bi-directional electric motor driving a drive screw. A shaft
coupler is threaded onto the drive screw. The shaft coupler is
splined to a stationary coupler retainer to prevent rotational
movement thereof. The shaft coupler is connected to a hydraulic
piston slidably mounted within a pressure chamber by a compression
spring. The spring functions both as a damper and as accumulator in
a hydraulic system to help stabilize hydraulic pressure. An
electrical control system for the hydraulic actuator comprises a
high-pressure cutoff switch, a low-pressure cutoff switch, and a
control switch. The control switch is adapted for activating the
hydraulic actuator assembly and selecting desired operation
mode.
Inventors: |
Krisher; James A. (Fort Wayne,
IN) |
Assignee: |
Spicer Technology, Inc. (Fort
Wayne, IN)
|
Family
ID: |
24209200 |
Appl.
No.: |
09/553,384 |
Filed: |
April 20, 2000 |
Current U.S.
Class: |
92/130R;
92/140 |
Current CPC
Class: |
B60T
8/326 (20130101); B60T 8/489 (20130101); B60T
13/745 (20130101) |
Current International
Class: |
B60T
13/74 (20060101); B60T 13/00 (20060101); B60T
8/48 (20060101); B60T 8/32 (20060101); F01B
031/00 (); F01B 009/00 () |
Field of
Search: |
;92/3,31,32,13R,136,140
;60/545,534,431 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ryznic; John
Attorney, Agent or Firm: Liniak, Berenato, Longacre &
White
Claims
What is claimed is:
1. A hydraulic actuator assembly, comprising:
a housing having an axial bore therethough;
a selectively controllable non-rotatable shaft coupler adapted to
reciprocate within said bore;
a hydraulic piston slidably mounted within said bore; and
a spring element abutting said shaft coupler at one end and said
piston at the other end thereof so that when said shaft coupler
being moved said spring element urging said piston to move.
2. The hydraulic actuator assembly as defined in claim 1, further
including a drive screw mounted within said bore in said housing
for driving said coupler.
3. The hydraulic actuator assembly as defined in claim 2, further
including a drive motor connected to said housing, said motor
having an output shaft drivingly connected to said drive screw.
4. The hydraulic actuator assembly as defined in claim 3, wherein
said drive motor is a bi-directional electric motor.
5. The hydraulic actuator assembly as defined in claim 3, further
comprising a gear reducer disposed between said drive screw and
said output shaft of said drive motor.
6. The hydraulic actuator assembly as defined in claim 1, wherein
said coupler is non-rotatably connected to said housing.
7. The hydraulic actuator assembly as defined in claim 6, further
including splines formed on a part of an inner peripheral surface
of said bore engaging splines formed on at least part of an outer
peripheral surface of said coupler.
8. The hydraulic actuator assembly as defined in claim 1, further
including a stationary coupler retainer encasing said coupler and
non-rotatably connected thereto, said stationary coupler retainer
is fixed to said housing.
9. The hydraulic actuator assembly as defined in claim 8, wherein
said coupler retainer includes splines formed on an inner
peripheral surface of said retainer engaging splines formed of at
least part of an exterior peripheral surface of said shaft
coupler.
10. The hydraulic actuator assembly as defined in claim 1, wherein
said spring element is a coil spring.
11. The hydraulic actuator assembly as defined in claim 2, wherein
said spring element is a coil spring disposed about said drive
screw.
12. The hydraulic actuator assembly as defined in claim 4, further
comprising an electric motor control system including a first
pressure cutoff switch including a first pressure sensor and a
device to disable said electric motor when a first predetermined
pressure is detected by said sensor.
13. The hydraulic actuator assembly as defined in claim 12, wherein
said electric motor control system further includes a second
pressure cutoff switch including a second pressure sensor and a
device to disable said electric motor when a second predetermined
pressure is detected by said sensor, wherein the first
predetermined pressure is higher than the second predetermined
pressure.
14. The hydraulic actuator assembly as defined in claim 13, wherein
said electric motor control system further including a control
switch device alternately activating said first and second pressure
cutoff switches.
15. A hydraulic actuator assembly, comprising:
a housing forming an axial bore therethrough;
a bi-directional electric drive motor fixed to said housing;
a gear reducer drivingly connected to said electric motor;
a drive screw mounted within said bore in said housing and
drivingly connected to said gear reducer;
a non-rotatable shaft coupler threaded on said drive screw so that
a rotational motion of said drive screw being transformed to a
linear motion of said shaft coupler, said shaft coupler having
splines formed on at least part of an outer peripheral surface
thereof;
a stationary coupler retainer encasing said shaft coupler and fixed
to said housing, said coupler retainer provided with splines formed
on an inner peripheral surface thereof engaging said splines formed
on said exterior peripheral surface of said shaft coupler;
a hydraulic piston slidably mounted within said bore;
a compression spring element connected between said shaft coupler
and said piston so that when said shaft coupler being moved said
spring element urging said piston to move;
a first pressure cutoff switch including a first pressure sensor
and a means to disable said electric motor when a first
predetermined pressure being detected by said sensor;
a second pressure cutoff switch including a second pressure sensor
and a means to disable said electric motor when a second
predetermined pressure being detected by said sensor, the first
predetermined pressure being higher than the second predetermined
pressure; and
a control switch device alternately activating said first and
second pressure cutoff switches.
16. A hydraulic actuator assembly, comprising:
a housing forming an axial bore therethrough;
said bore including splines formed on a part of an inner peripheral
surface thereof;
a bi-directional electric drive motor fixed to said housing;
a gear reducer drivingly connected to said electric motor;
a drive screw mounted within said bore in said housing and
drivingly connected to said gear reducer;
a non-rotatable shaft coupler threaded on said drive screw so that
a rotational motion of said drive screw being transformed to a
linear motion of said shaft coupler, said shaft coupler having
splines formed on at least part of an outer peripheral surface
thereof engaging said splines formed on said inner peripheral
surface of said bore;
a hydraulic piston slidably mounted within said bore;
a compression spring element connected between said shaft coupler
and said piston so that when said shaft coupler being moved said
spring element urging said piston to move;
a first pressure cutoff switch including a first pressure sensor
and a means to disable said electric motor when a first
predetermined pressure being detected by said sensor;
a second pressure cutoff switch including a second pressure sensor
and a means to disable said electric motor when a second
predetermined pressure being detected by said sensor, the first
predetermined pressure being higher than the second predetermined
pressure; and
a control switch device alternately activating said first and
second pressure cutoff switches.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hydraulic actuators, and more
particularly to a hydraulic actuator assembly actuated by an
electric motor.
2. Description of the Prior Art
Hydraulic actuators are widely employed in various applications as
a source of a pressurized hydraulic fluid. Especially popular are
hydraulic actuators driven by an electric motor. These actuators,
typically, include a motor driven screw shaft, a non-rotatable nut
threaded to the screw shaft, and a hydraulic piston slidably
mounted within a hydraulic cylinder and fixed to the nut. When the
electric motor is actuated, the rotary motion of the screw shaft is
transmitted to the nut that linearly travels along the screw shaft.
Since the piston is fixed to the nut, it also moves along the screw
shaft, thus generating a desired hydraulic pressure. However, since
hydraulic fluid is practically incompressible, the fluctuation of
the fluid pressure in a hydraulic system could be extremely large
due to even small changes in a volume of the hydraulic cylinder. To
cure this problem, hydraulic dampers and/or hydraulic accumulators
are, typically, installed in the hydraulic system, increasing the
cost and complexity of the hydraulic system.
SUMMARY OF THE INVENTION
The present invention provides an improved hydraulic pressure
actuator assembly that includes an integral damper/accumulator and
a low cost control system.
The hydraulic actuator assembly of the present invention comprises
a bi-directional electric motor driving a drive screw shaft through
a gear reducer. A shaft coupler is threaded onto the drive screw
shaft. The shaft coupler is splined to a stationary coupler
retainer to prevent rotational movement thereof. The shaft coupler
is connected to a hydraulic piston slidably mounted within a
pressure chamber by a compression spring. Thus, when the electric
drive motor is actuated by a signal from a control unit, the gear
reducer rotates the drive screw. The rotary motion of the drive
screw is transmitted to the shaft coupler which travels linearly
along the drive screw as the spline fit between the shaft coupler
and the coupler retainer prevents the coupler from rotating. The
linear axial motion of the shaft coupler is transmitted to the
hydraulic piston via the compression spring thereby generating a
pressurized hydraulic fluid in a pressure chamber.
The compression spring of the hydraulic actuator functions both as
a damper and as accumulator in a hydraulic system to help stabilize
hydraulic pressure and to minimize system pressure loss after the
motor stops.
An electrical control system for the hydraulic actuator comprises a
high-pressure cutoff switch, a low-pressure cutoff switch, and a
control switch. The control switch is adapted for activating the
hydraulic actuator assembly and selecting the desired operation
mode.
Thus, the present invention reduces production cost of the
hydraulic system by eliminating separate hydraulic dampers and
accumulators and reduces labor cost by eliminating the operation of
installing those separate components in the system.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent
from a study of the following specification when viewed in light of
the accompanying drawings, wherein:
FIG. 1 is a sectional view of a hydraulic actuator assembly in
accordance with the first preferred embodiment of the present
invention;
FIG. 2 is a sectional view of a hydraulic actuator assembly in
accordance with the second preferred embodiment of the present
invention;
FIG. 3 is a schematic diagram showing a hydraulic actuator control
system in accordance with the preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The preferred embodiment of the present invention will now be
described with the reference to accompanying drawings.
FIG. 1 of the drawings illustrates a novel arrangement of hydraulic
actuator 10 in accordance with a first preferred embodiment of the
present invention. Reference numeral 12 defines a housing provided
with an axial bore 14 therethrough and a communication opening 14'.
The axial bore 14 includes a cylindrical hydraulic
pressure-generating chamber 15. The pressure chamber 15 includes a
provision for a pressure line (not shown) at the end thereof via
the communication opening 14' for attachment to any hydraulically
actuated mechanism, such as, for example, a hydraulic brake
system.
The hydraulic actuator 10 is powered by a bi-directional electric
motor 16 having an output shaft (not shown). The output shaft of
the hydraulic actuator 10 is drivingly connected to a drive screw
20 via a gear reducer 18. The drive screw 20 is disposed inside the
housing 12 coaxially therewith. The electric motor 16 and the gear
reducer 18 are secured to the housing 12 by means of fasteners 13.
A non-rotatable shaft coupler 22 is linearly driven by the drive
screw 20. Preferably, this is achieved by providing a portion of an
inner peripheral surface of the bore 14 of the housing 12 with
splines 12' engaging corresponding external splines 23 formed on
the shaft coupler 22. Thus, the shaft coupler 22 is prevented from
rotating while allowed to move linearly within the bore 14.
Alternatively, the bore 14 may be provided with a groove (not
shown) along the axial direction of the drive screw 20 for
receiving a key element (not shown) extending radially outwardly
from the shaft coupler 22 to prevent the shaft coupler 22 from
rotating when the drive screw 20 rotates. Such arrangement is well
known in the art. Those of ordinary skill in the art will
appreciate that there are many other equivalent means that could be
used for the same purpose.
Preferably, the shaft coupler 22 is threadably engaged with the
drive screw 20 through a conventional ball-screw mechanism (not
shown) well known to those skilled in the art. Thus, rotational
motion of the drive screw 20 is transformed to a linear motion of
the shaft coupler 22.
A hydraulic piston 26 is slidably mounted in the
pressure-generating chamber 15. The shaft coupler 22 is connected
to the piston 26 by a compression spring element 28 transmitting
the axial motion of the shaft coupler 22 to the piston 26.
Preferably, a cylindrical coil spring is employed.
With the arrangement of the hydraulic actuator assembly 10
described above, when the motor 10 is actuated by a signal from any
appropriate control unit (not shown), the gear reducer 18 rotates
the drive screw 20. The rotary motion of the drive screw 20 is
transmitted to the shaft coupler 22 which travels linearly along
the drive screw 20 downward in FIG. 1 as the spline fit between the
shaft coupler 22 and the housing 12 prevents the coupler 22 from
rotating with the drive screw 20. The linear axial motion of the
shaft coupler 22 is transmitted to the hydraulic piston 26 via the
compression spring 28 thereby to cause the hydraulic pressure
generating chamber 15 to generate a pressurized hydraulic
fluid.
In the hydraulic actuator assembly 10 of the present invention, the
compression spring 28 not only couples the shaft coupler 22 and the
piston 26, but also functions as both a damper and accumulator in a
hydraulic system it is employed, in order to stabilize hydraulic
pressure in the system. Since hydraulic fluid is practically
incompressible, the fluctuation of the fluid pressure in the
hydraulic system could be extremely large due to even small changes
in a volume of the pressure chamber 15. The compression spring
provides for an expansion of the volume of the pressure chamber 15,
reducing the necessity for critical motor stop timing to prevent
over-pressurization of the hydraulic system. Moreover, the
compression spring 28 functions as an accumulator to minimize
system pressure loss after the motor 16 stops. This particular
feature prevents a substantial system pressure loss in case of
small volume changes in the pressure chamber 15 during the
operation that could be attributed to movement/repositioning of
components of the actuator assembly 10, or the hydraulic system
being pressurized.
FIG. 2 illustrates a second preferred embodiment of the present
invention. In this figure, parts corresponding to those of FIG. 1
have been designated by the same reference numerals.
In this embodiment, fixedly secured within the housing 12 is a
stationary coupler retainer 24 that prevents rotational movement of
the shaft coupler 22, but allows linear movement thereof. In the
preferred embodiment, the coupler retainer 24 is provided with
internal splines 25 engaging corresponding external splines 23
formed on the shaft coupler 22. Alternatively, the coupler retainer
24 may be provided with a groove (not shown) along the axial
direction of the drive screw 20 for receiving a key element (not
shown) extending radially outwardly from the shaft coupler 22 to
prevent the shaft coupler 22 from rotating when the drive screw 20
rotates. Such arrangements are well known to those skilled in the
art. Other appropriate arrangements for preventing rotation of the
shaft coupler 22 during the rotation of the drive screw 20, well
known in the prior art, are also within the scope of the present
invention.
FIG. 3 illustrates schematic diagram showing a hydraulic actuator
control system 30 in accordance with the preferred embodiment of
the present invention. The control system 30 of the hydraulic
actuator 10 comprises a first or high pressure cutoff switch 32, a
second or low pressure cutoff switch 34, and a control switch
device in the form of a double pole/double throw (DPDT) toggle
switch 36. The DPDT switch 36 is adapted for activating the
hydraulic actuator assembly 10 and selecting desired operation
mode. Both pressure cutoff switches 32 and 34 are attached to the
housing 12 of the actuator assembly 10.
As illustrated in detail in FIGS. 1 and 2, the high pressure cutoff
switch 32 includes a first or high pressure sensor 32' provided in
the pressure chamber 15, and a device 32" to disable the electric
motor 16 when a predetermined high pressure is detected by the
sensor 32'. Correspondingly, the low pressure cutoff switch 34
includes a second or low pressure sensor 34' provided in the
pressure chamber 15, and a device 34" to disable the electric motor
16 when a predetermined low pressure is detected by the sensor
341.
In operation, in order to increase the pressure of the hydraulic
fluid, the DPDT switch 36 is toggled to the ON mode and the motor
16 is activated to increase the fluid pressure until the high
pressure cutoff switch 32 disables the motor 16 when the
predetermined high pressure is detected by the sensor 32'. When the
DPDT switch 36 is toggled to the OFF mode, current is reversed to
the motor and the piston 26 moves in the opposite direction to
reduce the fluid pressure until the low pressure cutoff switch 34
disables the motor 16 when the predetermined low pressure is
detected by the sensor 34'.
The DPDT switch 36 may be toggled manually or controlled
automatically by an appropriate control device that may include an
ECU and a number of necessary control sensors. Similar control
devices are well known in the art.
Therefore, the actuator assembly in accordance with the present
invention represents a novel arrangement of the hydraulic actuator
provided with an integral fluid damper/actuator adapted to
stabilize fluid operating pressure in a hydraulic system.
The foregoing description of the preferred embodiments of the
present invention has been presented for the purpose of
illustration in accordance with the provisions of the Patent
Statutes. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obvious modifications or
variations are possible in light of the above teachings. The
embodiments disclosed hereinabove were chosen in order to best
illustrate the principles of the present invention and its
practical application to thereby enable those of ordinary skill in
the art to best utilize the invention in various embodiments and
with various modifications as are suited to the particular use
contemplated, as long as the principles described herein are
followed. Thus, changes can be made in the above-described
invention without departing from the intent and scope thereof. It
is also intended that the scope of the present invention be defined
by the claims. appended thereto.
* * * * *